SKYLIGHTS
Astronomy news for the week starting Friday, July 27, 2001.
We begin the week with the Moon passing its first quarter. For the
next seven days it will wax through gibbous, getting brighter each
night as it moves at its 13 degree-per-day pace against the
background stars. Since the Sun is now moving through the
northerly constellations of the Zodiac (this week in Cancer), the
Moon -- as it approaches full -- passes through the southerly
constellations, bottoming out in Sagittarius the night of
Wednesday, August 1.
Aside from the Moon, the evening sky is dominated by reddish Mars,
the next planet out from the Earth. Shining from southern
Ophiuchus (between the classic zodiacal constellations of Scorpius
and Sagittarius), the planet is slowly picking up easterly speed
against the background stars. The tilt of its orbit has sent it
several degrees below the ecliptic (the apparent solar path), while
the tilt of the lunar orbit has sent the Moon just north of it. As
a result, as the Moon approaches Mars the night of Sunday the 29th,
the Moon will be some 6 degrees to the north, just greater than the
spread between the front bowl stars (the "Pointers") of the Big
Dipper (which in the evening is now descending the sky to the
northwest). The morning, on the other hand, is dominated by the
mythological opposite of the "god of war," Venus, the "goddess of
love and beauty," which is strikingly lovely in the morning hours
to the east before dawn.
It is dim Neptune's week, however, as the farthest of the large
planets passes through opposition to the Sun on Monday, July 30, as
it moves retrograde in Capricornus. Discovered in 1846 as a result
of its gravitational influence on Uranus, Neptune has yet to make
a full orbit since found, as it takes 165 years to make a complete
circuit of the Sun. (It will come full circle in 2011.) Of the
traditional planets of the Solar System (including tiny Pluto,
which now hangs out in Ophiuchus 15 degrees almost exactly to the
north of Mars), only Neptune and Pluto require a telescope to see,
Uranus (somewhat to the east of Neptune) faintly visible to the
naked eye.
As July moves into August, we find Scorpius on the meridian to the
south as evening descends. Part of a "double constellation," the
scorpion's claws stretch out to the west as the bright stars of
Libra (the celestial scales), Zubenelgenubi the southern claw,
Zubeneschamali the northern. Two and a half thousand years ago the
"Balance" held the autumnal equinox (the point where the Sun
crosses the celestial equator on its way south). Precession, the
26,000 year wobble of the Earth's axis, has long since moved it
westerly into Virgo, just as it has moved the vernal equinox (where
the Sun moves north of the equator) from Aries into Pisces.
